Transverse Vibration and Stability Analysis of Circular Plate Subjected to Follower Force and Thermal Load

Transverse vibration and stability analysis of circular plate subjected to follower force and thermal load are analyzed.Based on the thin plate theory in involving the variable temperature,the differential equation of transverse vibration for the axisymmetric circular plate subjected to follower force and thermal load is established.Then,the differential equation of vibration and corresponding boundary conditions are discretized by the differential quadrature method.Meanwhile,the generalized eigenvalue under three different boundary conditions are calculated.In this case,the change curve of the first order dimensionless complex frequency of the circular plate subjected to the follower force in the different conditions with the variable temperature coefficient and temperature load is analyzed.The stability and corresponding critical loads of the circular plate subjected to follower force and thermal load with simply supported edge,clamped edge and free edge are discussed.The results provide theoretical basis for improving the dynamic stability of the circular plate.

Transverse Stability in the Discrete Inductance-Capacitance Electrical Network

This work investigates the dynamics of modulated waves in a coupled nonlinear LC transmission line. By means of a method based on the semi-discrete limit and in suitably scaled coordinates, we derive the two-dimensional NLS equation governing the propagation of slowly modulated waves in the network. The exact transverse solution is found and the analytical criteria of stability of this solution are derived. The condition for which the network can exhibit modulational instability is also determined. The exactness of this analytical analysis is confirmed by numerical simulations performed on the exact equation of the network.

Stability for basic system of equations of atmospheric rhotion

The topological characteristics for the basic system of equations of atmospheric motion were analyzed with the help of method provided by stratification theory. It was proved that in the local rectangular coordinate system the basic system of equations of atmospheric motion is stable in infinitely differentiable function class. In the sense of local solution, the necessary and sufficient conditions by which the typical problem for determining solution is well posed were also given. Such problems as something about ＂speculating future from past＂ in atmospheric dynamics and how to amend the conditions for determining solution as well as the choice of underlying surface when involving the practical application were further discussed. It is also pointed out that under the usual conditions, three motion equations and continuity equation in the basic system of equations determine entirely the property of this system of equations.

Drag Optimization of A Planing Vessel Based on the Stability Criteria Limits

One of the important phases of designing a craft is stability analysis and optimization of the drag force in cruise speed. In this research the longitudinal and lateral stability of a planing hull craft (DTMB 62 model 4667-1) is investigated with some semi-empirical formulae and the effects of some important design parameters are investigated on the limit of stability region. Also on the basis of these empirical formulations and by using a genetic algorithm the drag force is optimized in each constant cruise speed with the stability criteria limits at a constant beam or projected area. Aspect ratio, the longitudinal position of the gravity center and deadrise angle are the optimization parameters. The results show that the aspect ratio and the longitudinal position of the gravity center are two important parameters in optimizing the drag force and for this planing vessel the drag force can be reduced by 22%.

Dynamic Stability of Viscoelastic Plates with Finite Deformation and Shear Effects

Based on Reddy's theory of plates with higher order shear deformations and the Boltzmann superposition principles, the governing equations were established for dynamic stability of viscoelastic plates with finite deformations taking account of shear effects. The Galerkin method was applied to simplify the set of equations. The numerical methods in nonlinear dynamics were used to solve the simplified system. It could be seen that there are plenty of dynamic properties for this kind of viscoelastic plates under transverse harmonic loads. The influences of the transverse shear deformations and material parameter on the dynamic behavior of nonlinear viscoelastic plates were investigated.

(r, s)-STABILITY OF UNFOLDING OF г-EQUIVARIANT BIFURCATION PROBLEM

In this paper,the (?)-equivariant (s, t)-equivalence relation and (?)-equivariant infinitesimally (r, s)-stability of (?)-equivariant bifurcation problem are defined. The criterion for (?)-equivariant infinitesimally (r, s)-stability is proven when (?) is a compact finite Lie group .Transversality condition is used to characterize the stability.

圆形截面罐体液体晃动的摆锤模型可行性研究

为研究圆形截面罐体液罐车液体晃动等效摆锤模型的可行性,运用非惯性系下流体Euler方程和均质平面体质心计算公式,构建了液体自由液面倾斜率和质心坐标精确计算模型。得出圆形截面罐体液罐车在横向加速度作用下,液体质心运动轨迹是以罐体截面中心为圆心的一段圆弧,在此基础上提出了一种以液体质心与罐体中心连线为等效摆长的摆锤模型。采用理论计算与计算流体力学(computational fluid dynamics, CFD)仿真技术,分别得到相对应条件下的摆锤振动曲线图像。摆锤振动曲线图像表明,将圆形截面罐体液罐车液体晃动视为摆锤振动具有可行性,可以较好地反映出液体晃动变化规律,方便计算液体晃动时对罐体内壁的反作用力。研究结论可为开展液罐车横向稳定性研究提供理论参考。

国内海上航行油船破损稳性争议点浅析

针对船检机构在日常审图工作中遇到的油船破损稳性计算不符合要求的问题,开展原因分析。以国内某海上航行油船为例,重点探讨确定艏尖舱区域破损范围时应遵照的分舱依据,并针对该案例船破损稳性计算存在的缺陷提出改进建议,为船检机构和验船师开展油船破损稳性研究及统一检验标准提供参考。

Finite element analysis for wellbore stability of transversely isotropic rock with hydraulic-mechanical-damage coupling

The finite element analysis （FEA） technology by hydraulic-mechanical-damage （HMD） coupling is proposed in this paper for wellbore stability analysis of transversely isotropic rock, developed basing on the recently established FEA technology for iso- tropic rock. The finite element （FE） solutions of numerical wellbore model, damage tensor calculation and Pariseau strength criterion for transversely isotropic rock are developed for researching the wellbore failure characteristics and computing the collapse and fracture pressure of laminated rock as shale reservoirs. The classic Blot constitutive for rock as porous medium is introduced to establish a set of FE equations coupling with elastic solid deformation and seepage flow. To be in accord with the inclined wellbore situation, the coordinate transformation for global, wellbore, in-situ stress and transversely isotropic for- mation coordinate systems is established for describing the in-situ stress field and the results in laminated rock. To be in accord with the practical situation, a three-dimensional FIE model is developed, in which several other auxiliary technologies are com- prehensively utilized, e.g., the typical Weibull distribution function for heterogeneous material description and adaptive tech- nology for mesh refinement. The damage tensor calculation technology for transversely isotropic rock are realized from the well-developed continuum damage variable of isotropic rock. The rock is subsequently developed into a novel conceptual and practical model considering the stress and permeability with the damage. The proposed method utilizing Parisean strength cri- terion fully reflects the strength parameters parallel or perpendicular to bedding of the transversely isotropic rock. To this end, an effective and reliable numerically three-step FEA strategy is well established. Numerical examples are given to show that the proposed method can establish efficient and applicable FE model and be suitable for analyzing the state of pore pressure and stress surrounding wellbore, furthermore to demonstrate the effectiveness and reliability of the instability analysis of wellbore failure region and the safe mud weight computation for collapse and fracture pressure of transversely isotropic rock.

Finite element analysis for inclined wellbore stability of transversely iso-tropic rock with HMCD coupling based on weak plane strength criterion

The finite element analysis(FEA) technology by hydraulic-mechanical-chemical-damage(HMCD) coupling is proposed in this paper for inclined wellbore stability analysis of water-sensitive and laminated rock, developed basing on the recently established FEA technology for transversely isotropic rock with hydraulic-mechanical-damage(HMD) coupling. The chemical activity of the drilling fluid is considered as phenomenological hydration behavior, the moisture content and parameters of rock considering hydration could be determined with time. The finite element(FE) solutions of numerical wellbore model considering the chemical activity of drilling fluid, damage tensor calculation and weak plane strength criterion for transversely isotropic rock are developed for researching the wellbore failure characteristics and computing the time-dependent collapse and fracture pressure of laminated rock as shale reservoirs. A three-dimensional FE model and elastic solid deformation and seepage flow coupled equations are developed, and the damage tensor calculation technology for transversely isotropic rock are realized by introducing effect of the hydration and the stress state under the current load. The proposed method utilizing weak plane strength criterion fully reflects the strength parameters in rock matrix and weak plane. To the end, an effective and reliable numerically three-step FEA strategy is well established for wellbore stability analysis. Numerical examples are given to show that the proposed method can establish efficient and applicable FE model and be suitable for analyzing the timedependsolutions of pore pressure and stresses, and the evolution region considering the hydration surrounding wellbore,furthermore to compute the collapse cycling time and the safe mud weight for collapse and fracture pressure of transversely isotropic rock.

THE TRANSVERSAL GEOMETRIC EFFECTS IN A FREE ELECTRON LASER

The effects of a beam thickness and a conducting wall in a free electron laser with a linearlypolarized wiggler magnetic field and an axial magnetic field are investigated within the framework of fluid-Maxwell equations.The growth rate of free electron laser instability is obtained,in which the nonlinear bulkand surface current density are simultaneously considered.The numerical calculations indicate that the bulkcoupling is dominant.There is an optimum beam thickness and separation between the conducting walls forwhich the growth rate is maximum.

系杆拱桥稳定性分析

研究各种设计工况下的系杆拱桥的稳定性,以一座混凝土系杆拱桥为例,依据结构弹性屈曲理论,求解了系杆拱桥的主要屈曲模态,分析了横撑设置位置及设置形式对稳定性的影响,分析了系杆拱桥施工阶段和运营阶段静力稳定性的最不利荷载工况并求解了稳定特征值,采用一阶模态下附加初始缺陷的非线性分析方法求解了地震工况下的稳定性。分析结果表明:拱肋横桥向屈曲为系杆拱桥的主要失稳模态,屈曲时横向最大位移点在拱肋结构的等分点处;横撑形式及布设位置对横向稳定性的提高有显著作用,“一”字撑、“K”字撑、“米”字撑提高作用依次提升;系杆脱架阶段为施工阶段失稳的最不利工况,对称满跨布载为运营阶段失稳的最不利工况;E1、E2地震工况下屈曲特征值较恒载作用下分别降低了7.4%、13.3%,在高震区的动力稳定性应引起重视。

连通式横向减振器在地铁车辆上的适用性分析

随着地铁车辆运行速度等级的提高,受安装空间与成本限制,未安装抗蛇行减振器的快速地铁将出现车辆运行稳定性不足的问题,针对这一问题,提出一种连通式二系横向减振器,该减振器既能够提供横向减振的功能,又能达到抗蛇行减振的目的。基于连通式横向减振器的工作原理,建立了连通式横向减振器的数学模型以及更为准确的AMESim仿真模型,并分析了不同车辆运动状态下连通式横向减振器的阻尼特征。最后采用MATLAB/Simulink对连通式横向减振器模型与地铁车辆动力学模型进行联合仿真,研究了连通式横向减振器对车辆系统动力学性能的影响。仿真结果表明,连通式横向减振器在保证车辆直线运行平稳性及曲线通过安全性的条件下,大幅提高了车辆非线性临界速度,改善了地铁车辆的运行稳定性。

广州海心桥人致振动研究

海心桥为主跨198.152 m的钢结构曲梁斜拱人行桥,具有轻质、斜拱、空间曲线结构的特性,动力特性复杂,需对其进行人致振动研究。采用有限元软件MIDAS Civil建立空间有限元模型,根据德国人行桥设计指南EN03(2007)(简称德国EN03规范)和我国《城市人行天桥与人行地道技术规范》(CJJ 69—95)(征求意见稿)(简称我国规范征求意见稿),基于单自由度共振法分析了人致振动加速度峰值以评价该桥的人致振动舒适性,并基于Dallard公式确定人致横向动力失稳临界人数以分析该桥的横向动力稳定性。结果表明:该桥的主梁和拱肋刚度相近,存在竖向振动与横向振动耦合的动力特性,因此人致振动分析时充分考虑了两者的耦合作用;分别有13阶、9阶模态的竖向加速度和11阶、10阶模态的横向加速度不满足德国EN03规范、我国规范征求意见稿CL1舒适性标准;低阶频率下两规范计算的加速度峰值及舒适性评价结果接近,高阶频率下德国EN03规范计算的加速度峰值较大,舒适性评价结果更加保守;该桥1阶及3阶模态横向失稳临界人数对应人群密度均小于设计人群密度,当桥梁发生1阶或3阶振动时存在横向失稳的可能,加装TMD后横向稳定性满足要求。

大跨度变截面隧道施工工法数值模拟分析

针对后岭下隧道内引出联络线段设计跨度大、变截面横向扩挖尺寸长、安全风险高等特点,对三台阶临时仰拱法上台阶采用支立门架法和类正洞台阶法横向过渡扩挖的2种方案进行了数值模拟,即在10 m过渡段内上台阶分部开挖:纵向先、后行导坑开挖并架设竖向支撑,支点上部纵向加设连接梁或用槽钢将环向拱架纵连。然后拆除扩挖侧中间竖撑,形成横向扩挖门洞,扩挖施工中采取支立门架法防护或类正洞台阶法扩挖,并最终扩挖至拱脚,最后接长正洞环向拱架,完成过渡段上台阶施工。数值模拟分析结果表明,2种方法均安全可行,结合现场围岩实际情况,本工程采取了支立门架方案成功完成了扩挖,洞周土体变形的监测值和模拟值变化规律基本一致,土体位移与应力变化均小于模拟值,且在允许范围内。本案的成功实施为类似大跨度变截面隧道横向扩挖施工提供重要的参考和借鉴,具有重要的实用意义。

神经肌肉电刺激对躯干稳定肌影响的研究进展

该文从神经肌肉电刺激作用于躯干稳定肌的效果与参数及对不同人群的应用效能等角度,阐述了躯干稳定肌的组成与功能,以及神经肌肉电刺激招募躯干稳定肌的作用机制与参数,并分析探讨了其临床效果。未来的临床研究可能集中在健康人群的长期随访队列研究和运动损伤人群躯干稳定肌萎缩的机制与临床研究方面,同时神经肌肉电刺激联合运动康复的研究也是发展趋势。该文预判相关便携式NMES设备的研发与应用具有较大的临床意义。

基于EFD的巡逻艇运动横稳性影响因素研究

针对高速执法巡逻艇因火炮射击后坐力而导致的横向失稳问题,本文采用基于试验流体力学(EFD)的方法,对高速巡逻艇模型在航行中受外力冲击的运动横稳性进行敲击试验模拟。首先对巡逻艇模型开展静水面拖曳试验,选定敲击试验状态;然后开展不同重心高度、不同外力冲量、不同航速的敲击试验,研究以上因素对巡逻艇运动横稳性的影响规律。结果显示,模型重心高度越高、外力冲量越大、航速越低,将会导致巡逻艇模型的运动横稳性越差。研究表明,基于EFD的高速艇航行横稳性研究方法是可行的,对高速艇的型线优化设计及火炮系统选型具有重要意义。

多梁式工字钢-混凝土组合梁设计要点分析

以40 m跨径的多梁式工字钢-混凝土组合梁为研究对象,利用ANSYS通用有限元软件建立三维数值分析模型。分析焊钉的集束式布置与均布式布置、组合梁的滑移效应及跨间横梁的设置情况等条件对结构横向分布系数、剪力滞效应、桥面板横向弯曲及成桥过程稳定等方面的影响。总结并提出建议,以期为类似结构的设计提供参考。

连续刚构桥空心薄壁墩布置研究

我国西南地区地质地形情况十分复杂,多崇山峻岭、深谷沟壑。在此修建高速公路,大跨径、高墩桥梁占比较大,当墩高大于40m后多采用空心薄壁形式。为增强其高墩稳定性,设计中常在一定的位置设置横隔板。横隔板的设置会造成施工周期延长,因此需要合理进行横隔板的布置。针对芷江至铜仁(湘黔界)公路拖冲特大桥连续刚构,进行横隔板优化布置分析,为山区高墩横隔板的布置提供参考经验。

各向异性地层中斜井井壁失稳机理

深部层理性地层井壁稳定性必须考虑地层物理力学性质的各向异性,然而目前井壁稳定设计方面仍粗略地将其近似为各向同性体,使得预测的维持井壁稳定的坍塌压力和破裂压力不能满足安全钻井的需要。笔者在研究层理地层岩石力学特性的基础上,获得了一种考虑地层方向特性的井壁围岩应力分布公式,分析了横观各向同性地层的井壁应力分布特征,建立了新的斜井地层井壁稳定分析模型。研究结果表明,岩石的弹性模量、地应力和地层倾斜度的变化对井壁围岩的应力分布和坍塌、破裂压力均会产生影响,克服了常规各向同性井壁稳定分析模型不能准确预测层理性地层斜井井壁稳定的难题。因此在钻井施工设计当中,须根据地层特性选择合适的分析模型,以更好地指导现场实践。